Blind stitch sewing is a method wherein yarn or thread emerges as a seam on only one side of the tailored fabric, without appearing on the other side. This special sewing method is generally applied for example in attaching a patch pocket or an outer pocket on a suit fabric since pocket formation may desirably be finished without a seam line showing on the front of the finished suit.
Conventionally, blind stitch sewing is performed by swinging motions of a curved need1e which reciprocatingly pierce the tailored fabrics in a slanted or lateral direction as contrasted with a perpendicular reciprocating motion by a straight needle. Accordingly, the pressure applied to the tailored fabric should be very carefully adjusted so as not to very widely or so as not to change sharply during the sewing motion. Nonetheless, wide variations or sharp changes of fabric pressure are likely to take place because of changes in the thickness of the fabrics being sewn. Formation of a patch pocket or a dart on a jacket suit are typical examples wherein the above described difficulties occur.
Some devices and methods suited to blind stitch sewing are described in U.S. Pat. No. 4,577,570, issued Mar. 25, 1986, which describes how to drive a sewing needle so as to direct its instantaneous motions to the tangential line of sewing curvatures and also to a device for operating the reciprocating motions of a rod to press tailored fabrics in synchronism with the motion of a sewing needle. However, this patent does not concern itself with the problem of regulating the lowest return point of reciprocating motion of the rod commensurate with a change in the thickness of the fabrics being sewn.